Nitrate Paradigm Does Not Hold Up for Sugarcane

Abstract

Modern agriculture is based on the notion that nitrate is the main source of nitrogen (N) for crops, but nitrate is also the most mobile form of N and easily lost from soil. Efficient acquisition of nitrate by crops is therefore a prerequisite for avoiding off-site N pollution. Sugarcane is considered the most suitable tropical crop for biofuel production, but surprisingly high N fertilizer applications in main producer countries raise doubt about the sustainability of production and are at odds with a carbon-based crop. Examining reasons for the inefficient use of N fertilizer, we hypothesized that sugarcane resembles other giant tropical grasses which inhibit the production of nitrate in soil and differ from related grain crops with a confirmed ability to use nitrate. The results of our study support the hypothesis that N-replete sugarcane and ancestral species in the Andropogoneae supertribe strongly prefer ammonium over nitrate. Sugarcane differs from grain crops, sorghum and maize, which acquired both N sources equally well, while giant grass, Erianthus, displayed an intermediate ability to use nitrate. We conclude that discrimination against nitrate and a low capacity to store nitrate in shoots prevents commercial sugarcane varieties from taking advantage of the high nitrate concentrations in fertilized soils in the first three months of the growing season, leaving nitrate vulnerable to loss. Our study addresses a major caveat of sugarcane production and affords a strong basis for improvement through breeding cultivars with enhanced capacity to use nitrate as well as through agronomic measures that reduce nitrification in soil.

Otimização da análise da atividade da redutase do nitrato e sua caracterização em folhas de cana-de-açúcar

“…Esse resultado também foi relatado por Oliveira & Magalhães (1989). Robinson et al (2011) constataram que plantas de cana-de-açúcar absorvem preferencialmente amônio à nitrato em condições de similaridade nas concentrações de ambas as formas iônicas. O nitrato se acumula muito pouco em plantas de cana-de-açúcar, até mesmo quando aplicadas altas doses de N, o que sugere que é prontamente metabolizado ao chegar às folhas (Ishikawa et al, 2009).…”

Nitrous oxide emission and fertiliser nitrogen efficiency in a tropical sugarcane cropping system applied with different formulations of urea

“…-by sugarcane crops (Robinson et al 2011). The increased N uptake could have contributed to the increase in sugarcane yield for the 100N_NICU treatment compared with the 100N_U treatment.…”

Post-anthesis nitrate uptake is critical to yield and grain protein content in Sorghum bicolor

“…Relatively higher grain yields have been achieved in genotypes of Zea mays (maize) that accumulate more nitrate in early plant development, presumably because the stored nitrate is remobilized and assimilated during grain fill (Hirel et al, 2001). Similarly, Sorghum bicolor (sorghum), a related C4 grain crop of the Panicoideae subfamily of Poaceae, can accumulate nitrate in young shoots (Gleadow et al, 2016;Robinson et al, 2011). However, there is minimal information on nitrate accumulation in cereal crops, how stored nitrate impacts the N status over the plant's lifecycle, and ultimately, how nitrate stores could influence yield and grain protein.…”

“…Seedlings were thinned to one per pot prior to commencing nutrient application, nine days after sowing (DAS). Each pot received 100 mL of nutrient solution three days per week containing: 2 mM MgSO4; 2 mM CaSO4; 0.457 mM KH2PO4; 42.5 μM K2HPO4; 100 μM FeEDTA; 10 μM MnSO4; 10 μM H3BO3; 1 μM CuSO4; 2.5 μM ZnSO4; and 0.35 μM Na2MoO4 (Robinson et al, 2011). One of two nitrate treatments either 1mM KNO3 (+ 4.5 mM K2SO4; Low) or 10 mM KNO3 (High) complemented the basic nutrient solution.…”